1. Field of the Invention
The present invention relates to an acceleration sensor used in automobile air bag, anti-lock brake and navigation systems, or other consumer appliances.
2. Description of the Background Art
Recently, many automobiles have been equipped with an air bag system. One of the important devices constituting the air back system is an acceleration sensor for detecting impact. The acceleration sensor is a sensor device that converts the acceleration subject to an object, into an electrical signal and then outputs it.
At present, acceleration sensors are mostly formed as an electron device which contains a semiconductor substrate prepared by photolithography, etching, micromachining, and other techniques. In general, such an acceleration sensor includes an acceleration detecting chip that detects acceleration and outputs it as an electrical signal, and a signal processing chip that processes the output signal from the acceleration detecting chip, converts acceleration to a numerical data or the like, and outputs it.
Meanwhile, to meet demanding requirements of miniaturization and low cost, one which is encapsulated with resin is used to replace a metal case, as an acceleration sensor package.
FIGS. 22 and 23 illustrate one acceleration detecting chip provided in an acceleration sensor. FIG. 22 is a top plan view, and FIG. 23 is a sectional view taken along the line Cxe2x80x94C of FIG. 22. An acceleration detecting chip ACg comprises a semiconductor substrate SB that has on its surface an acceleration detecting part AS. For example, a silicon substrate is used for the semiconductor substrate SB.
The acceleration detecting part AS includes a movable electrode ME, and two fixed electrodes FE1 and FE2 disposed so as to surround the movable electrode ME. Each side and bottom of the fixed electrodes FE1 and FE2 is fixed to the surface of the semiconductor substrate SB, in order that these electrodes will not easily swing when the acceleration detecting chip ACg receives impact. On the other hand, the movable electrode ME is mostly unfixed on its bottom but fixed on its side alone, to the semiconductor substrate SB, so that it will easily swing with the impact in the direction indicated by the arrow xe2x80x9cPxe2x80x9d in FIG. 22.
On the surface of the semiconductor substrate SB, there are formed wiring layer ILc connected to the fixed electrode FE1, wiring layer ILd connected to the fixed electrode FE2, wiring layer ILe connected to the movable electrode ME, and pad electrodes PDa for wire bonding which are connected to the wiring layer ILc to ILe, respectively.
In the acceleration detecting chip ACg so constructed, when it receives the impact in the direction indicated by the arrow xe2x80x9cPxe2x80x9d in FIG. 22, the distance between the movable electrode ME and fixed electrode FE1 or FE2, is increased or decreased. This causes variations in the electrostatic capacitance value between the movable electrode ME and fixed electrode FE1, and that between the movable electrode ME and fixed electrode FE2. Therefore, according to the amount of the variations in the capacitance values, acceleration can be detected.
FIG. 24 illustrates an acceleration sensor formed by encapsulating, in a resin package PK, a die pad DPc (i.e., a seat for mounting chips) that mounts an acceleration detecting chip ACg and a signal processing chip SCg, together with leads LD. The acceleration detecting chip ACg and signal processing chip SCg are fixed to the die pad DPc by an insulative adhesive, such as silicone resin, epoxy resin, or low-melting glass. The signal processing chip SCg is equipped with a semiconductor substrate that has on its surface signal processing wiring layer, circuit elements, and the like (not shown). That is, FIG. 24 illustrates an acceleration sensor of a SOP (Small Outline Package) type.
On the surface of the signal processing chip SCg, there are formed pad electrodes PDb that receives the output from pad electrodes PDa of the acceleration detecting chip ACg, and pad electrodes PDc that outputs the processed signal via the leads LD to the exterior. There are formed bonding wires WR, composed of Au or the like, which connect the pad electrodes with the leads LD and the pad electrodes each other.
A protection cap CPd is disposed on the acceleration detecting chip ACg, to prevent the resin flowing into the position of the movable electrode ME, when encapsulating the resin package PK. The protection cap CPd has a conductivity, and also functions to shield the acceleration detecting part AS, with a ground potential fed from the exterior via pad electrodes PDf, which are disposed at a location other than that of the protection cap CPd on the acceleration detecting chip ACg.
In the conventional acceleration sensor shown in FIG. 24, the acceleration detecting chip ACg and signal processing chip SCg are provided in a parallel arrangement on the die pad DPc, it is thus forced to use a large die pad, making it difficult to reduce the size of the acceleration sensor.
According to a first aspect of the present invention, an acceleration sensor comprises an acceleration detecting chip including an acceleration detecting part having a movable part that shifts depending on acceleration, so that the chip outputs an electrical signal depending on the shift of the movable part; a signal processing chip having a through-hole and a circuit for processing the electrical signal from the acceleration detecting chip; and a die pad to which the acceleration detecting chip and the signal processing chip are adhered, wherein the acceleration detecting chip is disposed in the through-hole of the signal processing chip on the die pad.
Since the acceleration detecting chip is disposed in the through-hole of the signal processing chip, the area of the die pad can be lessened than if the acceleration detecting chip and signal processing chip were provided in a parallel arrangement on the die pad. This permits a reduction in the size of the acceleration sensor.
According to a second aspect, the acceleration sensor of the first aspect further comprises: a cap adhered to the signal processing chip so as to cover the through-hole; and a resin encapsulation package covering at least an adhesive portion between the signal processing chip and the cap.
With the resin encapsulation package, more miniaturization and lower cost can be achieved than would be the case with a metal package. In addition, by virtue of the cap, when forming the resin encapsulation package, there is no possibility of the resin flowing into the acceleration detecting part of the acceleration detecting chip.
Preferably, the acceleration detecting chip further comprises an electrode for outputting the electrical signal, and the signal processing chip further comprises an electrode connected via a bonding wire to the electrode of the acceleration detecting chip.
According to a third aspect, in the acceleration sensor of the second aspect, the cap is a plate-like and has a notch about its periphery; an electrical connection between the acceleration detecting chip and the signal processing chip is established at the notch; and the notch is filled with an insulating material.
It is able to realize an acceleration sensor of less thickness because the electrical connection between the acceleration detecting chip and signal processing chip is made at the notch disposed about the periphery of the plate-like cap.
According to a fourth aspect, the acceleration sensor of the first aspect further comprises: a cap adhered to the acceleration detecting chip so as to cover the acceleration detecting part of the acceleration detecting chip; and a resin encapsulation package covering at least an adhesive portion between the acceleration detecting chip and the cap.
With the resin encapsulation package, more miniaturization and lower cost can be achieved than would be the case with a metal package. In addition, by virtue of the cap, when forming the resin encapsulation package, there is no possibility of the resin flowing into the acceleration detecting part of the acceleration detecting chip.
Preferably, the acceleration detecting chip further comprises an electrode for outputting the electrical signal, and the signal processing chip further comprises an electrode connected via a bonding wire to the electrode of the acceleration detecting chip.
According to a fifth aspect, an acceleration sensor comprises: an acceleration detecting chip having a first main surface, a second main surface opposed to the first main surface, and an acceleration detecting part formed in the first main surface, the acceleration detecting part having a movable part that shifts depending on acceleration, so that the chip outputs an electrical signal depending on the shift of the movable part; a signal processing chip having a first main surface, a second main surface opposed to the first main surface, and a circuit that processes the electrical signal from the acceleration detecting chip; a die pad adhered to the second main surface of the acceleration detecting chip; and a resin encapsulation package. In this acceleration sensor, the second main surface of the signal processing chip covers the acceleration detecting part and is adhered to the first main surface of the acceleration detecting chip, and the resin encapsulation package covers at least an adhesive portion between the acceleration detecting chip and the signal processing chip.
Since the acceleration detecting chip is adhered on the second main surface thereof to the die pad, and the second main surface of the signal processing chip is adhered to the first main surface of the acceleration detecting chip, the area of the die pad can be lessened than if the acceleration detecting chip and signal processing chip were provided in a parallel arrangement on the die pad. This permits a reduction in the size of the acceleration sensor. Further, by virtue of the resin encapsulation package, more miniaturization and lower cost can be achieved than would be the case with a metal package. Furthermore, the second main surface of the signal processing chip covers the acceleration detecting part and is adhered to the first main surface of the acceleration detecting chip. Therefore, when forming the resin encapsulation package, there is no possibility of the resin flowing into the acceleration detecting part of the acceleration detecting chip. It is therefore unnecessary to provide a cap covering the acceleration detecting part, and the number of components is thus lessened to reduce the cost.
According to a sixth aspect, in the acceleration sensor of the fifth aspect, the second main surface of the signal processing chip has a concave, and the acceleration detecting part of the acceleration detecting chip is covered in the concave of the signal processing chip.
Since the acceleration detecting part is nested in the concave of the second main surface of the signal processing chip, the movable part can be kept away from the second main surface of the signal processing chip.
Preferably, the acceleration detecting chip further has on the first main surface an electrode for outputting the electrical signal, and the signal processing chip further has on the first main surface an electrode connected via a bonding wire to the electrode of the acceleration detecting chip.
According to a seventh aspect, in the acceleration sensor of the fifth aspect, the acceleration detecting chip further has on the first main surface a first electrode for outputting the electrical signal, a second electrode, and a third electrode that is electrically connected to the second electrode and not covered with the signal processing chip; and that the signal processing chip further has on the second main surface a first electrode connected to the first electrode of the acceleration detecting chip, and a second electrode connected to the second electrode of the acceleration detecting chip. In this acceleration sensor, the second main surface of the signal processing chip is adhered to the first main surface of the acceleration detecting chip, by adhesive that is applied in the form of a frame on the first main surface of the acceleration detecting chip, so as to surround at least the acceleration detecting part.
Since the signal processing chip is further equipped with the first electrode connected to the first electrode of the acceleration detecting chip, and the second electrode connected to the second electrode of the acceleration detecting chip, no bonding wire is needed for making the electrical connection between both chips. This permits an improvement in productivity, without causing any wire sweep which is liable to occur by the use of a bonding wire. Furthermore, the second main surface of the signal processing chip is fixed to the first main surface of the acceleration detecting chip, by adhesive that is applied in the form of a frame on the first main surface of the acceleration detecting chip, so as to surround at least the acceleration detecting part. Therefore, even if these chips cannot be close together, by the presence of the respective electrodes, when forming a resin encapsulation package, there is no possibility of the resin following into the acceleration detecting part. Thereby, it is unnecessary to provide a cap covering the acceleration detecting part, and the number of components is thus lessened to reduce the cost.
According to an eighth aspect, an acceleration sensor comprises: an acceleration detecting chip having a first main surface, a second main surface opposed to the first main surface, and an acceleration detecting part formed in the first main surface, the acceleration detecting part having a movable part that shifts depending on acceleration, so that the chip outputs an electrical signal depending on the shift of the movable part; a signal processing chip having a circuit for processing the electrical signal from the acceleration detecting chip; a die pad having a first main surface adhered to the first main surface of the acceleration detecting chip, and a second main surface opposed to the first main surface; and a resin encapsulation package covering at least an adhesive portion between the acceleration detecting chip and the die pad.
With the resin encapsulation package, more miniaturization and lower cost can be achieved than would be the case with a metal package. In addition, since the acceleration detecting chip is adhered, on the first main surface thereof, to the first main surface of the die pad, when forming the resin encapsulation package, there is no possibility of the resin flowing into the acceleration detecting part of the acceleration detecting chip. Thereby, it is unnecessary to provide a cap covering the acceleration detecting part, and the number of components is thus lessened to reduce the cost.
According to a ninth aspect, in the acceleration sensor of the eighth aspect, the signal processing chip is adhered to the second main surface of the die pad; that the die pad has a through-hole, and the acceleration detecting chip further has on the first main surface an electrode that is exposed in the through-hole of the die pad and outputs the electrical signal to the signal processing chip.
Since the acceleration detecting chip is adhered, on the first main surface thereof, to the first main surface of the die pad, and the signal processing chip is adhered to the second main surface of the die pad, the area of the die pad can be lessened than if the acceleration detecting chip and signal processing chip were provided in a parallel arrangement on the die pad. This permits a reduction in the size of the acceleration sensor. In addition, the acceleration detecting chip further has, on the first main surface thereof, the electrode for outputting an electrical signal which is exposed in the through-hole of the die pad. This enables to establish an electrical connection between the acceleration detecting chip and signal processing chip.
According to a tenth aspect, in the acceleration sensor of the eighth aspect, the acceleration detecting chip has on the first main surface a concave, and the acceleration detecting part is formed in the concave.
Since the acceleration detecting part is formed in the concave, the movable part can be kept away from the first main surface of the die pad.
According to an eleventh aspect, in the acceleration sensor of the eighth aspect, the signal processing chip is adhered to the second main surface of the acceleration detecting chip.
Since the signal processing chip is adhered on the second main surface of the acceleration detecting chip, the area of the die pad can be lessened than if the acceleration detecting chip and signal processing chip were provided in a parallel arrangement on the die pad. This permits a reduction in the size of the acceleration sensor.
Preferably, in the acceleration sensor of eleventh aspect, the acceleration detecting chip further has on the first main surface an electrode for outputting the electrical signal; the die pad further has on the first main surface a wiring layer connected to the electrode of the acceleration detecting chip; and the signal processing chip further has an electrode connected via a bonding wire to the wiring layer of the die pad.
According to a twelfth aspect, in the acceleration sensor of the ninth aspect, the first main surface of the acceleration detecting chip is adhered to the first main surface of the die pad, by adhesive that is applied in the form of a frame on the first main surface of the acceleration detecting chip, so as to surround at least the acceleration detecting part.
Since the first main surface of the acceleration detecting chip is adhered to the first main surface of the die pad, by the adhesive that is applied in the form of a frame to the first main surface of the acceleration detecting chip, so as to surround at least the acceleration detecting part, the movable part of the acceleration detecting part can be kept away from the first main surface of the die pad, by the amount of the thickness of the adhesive.
It is an object of the present invention to reduce the size of an acceleration sensor having an acceleration detecting chip and a signal processing chip, with an improvement in arrangement of these chips.